But in her new book, “Going Off Script,” Rancic saves her harshest digs for her former flame, “Sliders” actor Jerry O’Connell, whom she compares to Jekyll and Hyde.

Jerry O’Connell and Giuliana Rancic circa 2004.WireImage

The two met at the W Hotel in San Diego and struck up a passionate, devoted love affair — that is, until he cheated on her with Ginger Spice, a k a Geri Halliwell.

“I was being two-timed for one of the lesser Spices?” she writes. Confronted, O’Connell told her, “ ‘Yeah, I know. I’m so sorry. I don’t know what happened.’ He had as much emotion as the customer-service representative who tells you your bags missed the flight.”

A contrite O’Connell wooed her back and the two discussed plans for marriage until Maxim’s 100 Hottest Women party in 2004 (Rancic, then Giuliani DePandi, was No. 94). Also in attendance was model and “X-Men” actress Rebecca Romijn (No. 7).

O’Connell wandered off. “Little did I know he was in the VIP area, talking up Rebecca. As a prelude to feeling up Rebecca.”

A week later, he departed for Las Vegas and stopped returning her calls. When she confronted him at his home, he refused to buzz her up.

“Nope. Sorry, homegirl,” he said, ending their relationship with: “Things change, but you take care, OK?”

Geri HalliwellGetty Images

“Going Off Script: How I Survived a Crazy Childhood, Cancer, and Clooney’s 32 On-Screen Rejections,” out this week, was written before the implosion of “Fashion Police.”

In a prescient moment in the book, Giuliana notes, “It still sometimes amazes me what we can get away with on air. Sometimes I wish the producers had stopped us.”

Rancic has nothing but praise for her “Fashion Police” co-stars, in particular Rivers, who gave her advice while negotiating her contract: “Make sure you have photo approval — that’s probably more important than health insurance.”

But Rancic doesn’t shy away from celebs she’s tangled with, including Russell Crowe (who walked out of an interview) and singer Ariana Grande, who muscled her way onto Rancic’s mark and refused to move.

Grande, 21, was on the preferred left side shot, Rancic writes, “which BTW, would be the side I fought for 13 years to get. Earn your stripes, girl.”